1. Field of the Invention
The invention relates to a rotor position estimating device, electric motor control system and rotor position estimating method that estimate a rotor position of an electric motor including a salient-pole rotor.
2. Description of Related Art
In an electromotive vehicle (such as an electric vehicle and a hybrid vehicle) on which an alternating-current motor is mounted as a power source of the vehicle, a synchronous motor, such as a permanent magnet-type synchronous motor that uses a permanent magnet for a rotor, is used as the alternating-current motor. In addition, energization control over the synchronous motor is executed on the basis of information about the position of the rotor. In the energization control over the synchronous motor, currents that are respectively supplied to coils of respective phases of the synchronous motor are controlled on the basis of the information about the position of the rotor. Therefore, usually, a rotation position sensor, such as a resolver, that detects a rotor position is used.
However, as described above, with the configuration that detects the rotor position with the use of the rotation position sensor, there occurs an offset error due to an error in the mounting position of the rotation position sensor, and a rotor position that is detected by the rotation position sensor deviates from an actual rotor position. As a result, the accuracy of energization control over the synchronous motor may be decreased. Thus, it is required to estimate an actual rotor position of the synchronous motor and then to detect an offset error of the rotation position sensor on the basis of the estimated actual rotor position.
As a technique for estimating the rotor position of the synchronous motor, for example, Japanese Patent Application Publication No. 7-245981 (JP 7-245981 A) describes a magnetic pole position detecting device for an electric motor. The magnetic pole position detecting device detects electric motor currents at the time of applying alternating-current voltages to the electric motor with the use of a current detector and then estimates magnetic pole positions (rotor position) of the electric motor on the basis of the detected values of the current detector. According to JP 7-245981 A, the detected electric motor currents are separated into a parallel component and a perpendicular component with respect to the alternating-current voltages applied, and the magnetic pole positions of the electric motor are detected on the basis of at least one of the parallel component and perpendicular component of the electric motor currents.
In JP 7-245981 A, the detected values of the current detector are converted to a current vector, and the rotor position is estimated on the basis of the converted current vector. Therefore, when there is a deviation in the detected values of the current detector with respect to actual electric motor current values (actual current values), it is difficult to estimate an accurate rotor position. Thus, the accuracy of energization control over the synchronous motor may decrease.